1. Field
The subject invention is in the field of tubular apparatus used for conducting acoustical energy which can be converted to sound by ears, apparatus such as ear horns and the tubular communications systems formerly used on ships. In particular it is in the field of such apparatus as applied to stethoscopes, i.e. the flexible tube connecting the chest piece which picks up the acoustic energy to the ear pieces which are inserted in a user's ears. Most particularly it is in the field of such tubes which are assemblies and include a feature or features which insulate the interior, energy transmitting portion of the tube from (1) extraneous ambient acoustic energy sources such as physical contact on the exterior of the tube assembly, finger contacts being one example, and (2) sounds generated in the ambient area of the use of the stethoscope.
2. Prior Art
The most pertinent prior art in this most particular field and known to the inventor of the subject invention is U.S. Pat. No. 5,952,618, issued to Deslauries. This patent covers a stethoscope, part of which is a conduit assembly comprising a flexible outer tube made of a material having a first density and at least one inner tube made of a material having a second density which is greater than the first density. The first tube is made of an elastomer such as a polymer or neoprene and the second tube is made of metal, preferably steel and is a close wound spring so that the conduit assembly is flexible and tends to be self straightening and kink free. The purpose of this construction is to acoustically insulate the assembly. The attenuation of acoustic energy transmitted through the wall of the assembly is attributed to the difference in the densities of the materials. The inventor of the subject invention believes that (1) the attenuation in lower frequency ranges is based on mechanical/structural support of the elastic outer tube by the stiff inner tube, and (2) that attenuation in higher frequency ranges is based on the inherent internal damping characteristics of the assembly and that the internal damping is based on conversion of acoustic energy to heat by the minute frictional actions between the inner and outer tubes. The inventor of the subject invention further believes that the essentially corrugated inner surface of the inner tube has negative effects on the transmission of acoustic energy through the assembly and that the acoustic attenuation achieved in this prior art assembly can be improved. Accordingly, the objectives of the subject invention are to provide, for use on stethoscopes, an acoustically insulated flexible tube having a smooth interior and optimized acoustical insulation.